Hello Soongsc,
remember:
http://www.diyaudio.com/forums/attachment.php?s=&postid=1531292&stamp=1212610725
the pulse response I measured myself at home was given in message:
http://www.diyaudio.com/forums/showthread.php?postid=1527765#post1527765
Best regards from Paris, France
Jean-Michel Le Cléac'h
remember:
http://www.diyaudio.com/forums/attachment.php?s=&postid=1531292&stamp=1212610725
the pulse response I measured myself at home was given in message:
http://www.diyaudio.com/forums/showthread.php?postid=1527765#post1527765
Best regards from Paris, France
Jean-Michel Le Cléac'h
soongsc said:
Lynn Olson said:
Lynne
My waveguide theory does not make this assumption, that's key, and it is capable of analyzing the phase plug effects. I have done this. In fact this work led to several patents on the topic. You are correct that horn theory cannot consider anything that involves differences across the device, ala phase plugs.
soongsc said:
Lynne and Soongsc
I have published impulse responses both on and off axis see http://www.ai-audio.com/products_esp15.html
A message to all those patiently waiting for 425 horns: I picked up the outstanding orders from the shop today - they look a very nice job, and I will do my best to get them cut / flanged up / drilled / rubbed back / signed / boxed and sent asap. However it may take little while longer. Will post photos from horn-shed if there is interest. I quite enjoy lo-tech solutions to hi-fi.
best rgds, martin
best rgds, martin
Hello Soongsc,
No overlap (if I understood correctly your remark) but red curve is for TD2001 current driven and blue curve is for TD2001 voltage driven.
(You'll see that current drive should be preferred using the TD2001).
Best regards from Paris, France
Jean-Michel Le Cléac'h
No overlap (if I understood correctly your remark) but red curve is for TD2001 current driven and blue curve is for TD2001 voltage driven.
(You'll see that current drive should be preferred using the TD2001).
Best regards from Paris, France
Jean-Michel Le Cléac'h
soongsc said:
Lynn Olson said:
Hi Lynn:
Spherical enclosures can avoid that mode by being small enough that the magnet sits in the center of the cylendar. While this limits people to speakers with relatively low Vas, it's those type of drivers that find use in this application fairly often. This gives the cylendar an extremely diverse internal structure for standing waves.
I also find that combining a flat surface into a 'round' enclosure can go a long way. Obviously a tube is a problematic shape, but a half cylendar with a flat face opposing its opening should provide a pretty good variety of supported modes, which obviously prevents any 1 mode from really standing out. A single piece of flat wood spanning the width of a cylendar along its entire length would greatly reduce the challenges presented by the interior profile of this shape.
I think too much is being attributed to "shape" as regards interior modes. I did my PhD theseis on modes in non-rectangular rooms and these results would apply. The lowest mode is always independent of shape for shapes that are not extreme in any one dimension. Thus a sphere and a cube will have identical first modes (stricktly volume dependent) and these will be identical to any box shape that is not more than three or four times longer in one dimension than the others. Higher order modes will have a density of modes that depends only on volume as the frequency goes up. So for a fixed volume the first mode and the higher modes are shape independent. The modal layout for modes "in-between" will vary slightly with shape, but not dramatically, especially not if filled with internal structures like braces and magnets, absorption material, etc. So basically the internal modes are not highly dependent on shape.
But the external diffraction is dominated by shape. Thus the external aspects of shape are critical while the internal ones are so much so. It can be shown that a sphere has the least diffraction of any shape, but NOT if it is a sphere with a piston in it. This modification of the geometry makes other shapes perfered and in fact an Oblate Spheriod has less diffraction for a piston installed in it than a sphere. The sharp slope change at the edge of the disk diffracts, with an oblate spheriod this slope change can be elliminated.
How do I know all this? Torpedoes and submarines. A huge amount of work was done where I went to school on diffraction off of these devices - for obvious reasons. Self diffraction in a torpedo was the limiting factor in its ability to "hunt" its prey. And diffraction off of a submarine was the limiting factor in hiding from this hunter.
But the external diffraction is dominated by shape. Thus the external aspects of shape are critical while the internal ones are so much so. It can be shown that a sphere has the least diffraction of any shape, but NOT if it is a sphere with a piston in it. This modification of the geometry makes other shapes perfered and in fact an Oblate Spheriod has less diffraction for a piston installed in it than a sphere. The sharp slope change at the edge of the disk diffracts, with an oblate spheriod this slope change can be elliminated.
How do I know all this? Torpedoes and submarines. A huge amount of work was done where I went to school on diffraction off of these devices - for obvious reasons. Self diffraction in a torpedo was the limiting factor in its ability to "hunt" its prey. And diffraction off of a submarine was the limiting factor in hiding from this hunter.
soongsc said:
I'm not sure that I understand - if the "polar plots to be the same for a wide range of frequencies" is true, then don't the polars have to "be constant amplitude at different angles" if the axial response has constant amplitude? Are you saying that the amplitude should be flat at all axis angles, but not at the same amplitude as the axial response? This later IS the definition of Constant Directivity with a given narrow directivity, i.e. exactly what I design my waveguides to do.
Everyone from Floyd Toole, Sigfried Linkwitz, Sean Olive to myself agree that Constant Directivity is the goal. What we don't all agree on is what that directivity should be. Floyd says "wide", Sigfried says Bipolar (cosine), and I say narrow (less than cosine). It all comes down to what you believe the influence of the very early (first) reflections is. We all differ in this regard.
Hydrodynamics and acoustics are different. The bow is done mostly for hydrodynamic reasons, and it has to also work well while the ship is on the surface.
The minimum difraction shape for an object of a given length and cross-sectional area is that prolate spheriod that fits these dimensions. That is actually very close to a submarines shape - basically a fat cigar.
The minimum difraction shape for an object of a given length and cross-sectional area is that prolate spheriod that fits these dimensions. That is actually very close to a submarines shape - basically a fat cigar.
gedlee said:
Interesting post, Earl. I'll leave off the modal density but would love to hear some more information on the behavior of diffraction on the sphere+piston. I can understand that the driver edge would be a challenge but wouldn't this be a non-issue for most drivers, as it would be either above the passband, or within a more directional region?
For all practical purposes the difference between a sphere and an oblat speriod for a piston would be minimal. The way to think about the situation is to recognize that a piston can be analyzed exactly as a point source at the center and ring source at the edge which accounts for the diffraction of the disk edge. Now if this edge goes back, rather than being flat, then there will be slightly greater difraction at the edge. What this would do is narrow the directivity slightly depending on the source size to the sphere size.
Now if the enclosure was an oblate spheriod then at the edge the surface is flat and so there would be less diffraction here and the directivity would be the same as that of a piston in an infinite baffle.
So unless you are tracking the polar response very carefully, you won't see any difference in practice.
There was an interesting AES paper on pistons in spheres some years back and they showed how the edge handling does have an effect on directivity.
The thing with boxes is that the diffraction of sound off of an edge arrives after the sound from the driver, and hence is non-minimum phase and cannot be corrected (so much for DEQX!). Lidia and I also showed that this kind of thing can be audible, especially at higher SPL levels.
This is also true of a waveguide/horn where the edge diffraction is not in time step with the main wavefront and hence is also not minimum phase (the disk has the edge diffraction in time synch with the center point source, there is no delay and so it is minimum phase, but in actuality only if the disk is flat!)
Now if the enclosure was an oblate spheriod then at the edge the surface is flat and so there would be less diffraction here and the directivity would be the same as that of a piston in an infinite baffle.
So unless you are tracking the polar response very carefully, you won't see any difference in practice.
There was an interesting AES paper on pistons in spheres some years back and they showed how the edge handling does have an effect on directivity.
The thing with boxes is that the diffraction of sound off of an edge arrives after the sound from the driver, and hence is non-minimum phase and cannot be corrected (so much for DEQX!). Lidia and I also showed that this kind of thing can be audible, especially at higher SPL levels.
This is also true of a waveguide/horn where the edge diffraction is not in time step with the main wavefront and hence is also not minimum phase (the disk has the edge diffraction in time synch with the center point source, there is no delay and so it is minimum phase, but in actuality only if the disk is flat!)
dlr said:
Hi Dave, the rounded shape has to do with minimizing drag. The same thing applied to airfoils. You don't see sharp leading edges on subsonic airfoils. But go super sonic and a sharp edge is what you want, form a purely aerodynamics point of view.
I have to say that I like Earl's impulse response. I don't see a lot of high frequency noise on it. Not surprising considering the foam plug should act as a low pass filter.
Well, anyone can have their opinion, and people that have a long history in this industry are well respected. But, if you calculate the shift of ITD and IID when you move left and right from the listening location, these two cannot shift in the same manner when you have contant directivity. Your wave guide data shows the amplitude remains too constant within the range of +/-22.5 deg or so. This would be the most critical range where I would want the roll-off to exist because this is the range where most serious listening position is.gedlee said:
Now, if the polar plots showed roll-off off axis, then shift in ITD and IID will shift more closly with each other. If the polar plots were the same for a wide range of frequencies, then I would call the combination of these characteristic "Controlled Directivity".
I was actually waiting for you to add the calculations in relation with ITD/IID to your published paper as you mentioned you would a while back. But I got tired of waiting to I just investigated myself.
